An active matrix-type display device selects two-dimensionally arranged pixel circuits by row, and writes gradation voltages to the selected pixel circuits according to a video signal, thereby displaying an image. Such a display device is provided with a scanning signal line drive circuit including a shift register, in order to select the pixel circuits by row.
Further, as a method of downsizing display devices, there is known a method of monolithically forming a scanning signal line drive circuit on a display panel along with pixel circuits using a manufacturing process of forming TFTs (Thin Film Transistors) within the pixel circuit. The scanning signal line drive circuit is formed using an amorphous silicon TFT or a microcrystalline silicon TFT, for example. A display panel having a scanning signal line drive circuit monolithically formed is also referred to as a gate driver monolithic panel.
As a shift register included in the scanning signal line drive circuit, various circuits have been known conventionally (Patent Documents 1 to 4, for example). Patent Document 1 describes a shift register having a plurality of unit circuits 91 illustrated in FIG. 17 connected in series. This shift register is monolithically formed on a liquid crystal panel using amorphous silicon TFTs.